Diffusion transfer process for the manufacture of priniting plates



United States Patent 3,186,842 DIFFUSION TRANSFER PRQCESS FOR THE MANUFACTURE OF PRINTING PLATES Louis Maria De Haes and Paul Maria Cassiers, Mortsel- Antwerp, Andre Rott, Berchem-Antwerp, Albert Petrus Wagemans, Edegem-Antwerp, and Jozef Frans Willems, Wilrijk-Antwerp, Belgium, assignors to Gevaert Photo- Producten N.V., Mortsel, Belgium, a company of Belgium No Drawing. Filed Oct. 14, 1959, Ser. No. 846,257 Claims priority, application Great Britain, Get. 25, 1957, 33,431/57 16 Ciairns. (Cl. 9629) This application is a continuation-in-part of application, Serial No. 769,542, filed October 27, 1958, now abandoned.

The present invention relates to a new method for producing printing plates according to the silver halide diffusion transfer process. More particularly, the present invention relates to improvements in the manufacture of printing plates for letter-press printing, offset or lithoprinting, and photogravure printing by using a silver halide diffusion transfer process.

United States Patent No. 2,352,014 describes a process of photographic image transfer which comprises contacting a photographic silver halide layer, containing a developing solution and a developed photographic image in the presence of a silver halide solvent and a fogging agent, with a receiving material which is insensitive to light.

According to said United States patent, fogging agents, known to be substances capable of promoting the reduction of silver halide not exposed to light, will improve and accelerate the transfer process. These fogging agents belong to the class of products which act as reduction or crystallization nuclei for silver halide, such as colloidal silver, colloidal sulphur and metal sulphides, such as nickel sulphide, cobalt sulphide, etc., and usually are incorporated into the receiving material either during the manufacture of the latter or by impregnation of the finished receiving material. It is to be noted, however, that these fogging agents may belong to the class of substances which are not such reduction or crystallization nuclei themselves but may form such nuclei by interacton with the diffused silver halides either by reduction or by the formation of rather insoluble compounds.

The silver halide difiusion transfer process has also been used in the production of lithographic plates, wherein the receiving material is a suitable metallic sheet coated with a layer containing substances which act as reduction or crystallization nuclei, such as for instance silver sulphide, or form such nuclei by interacting with the diffusing silver salt complexes such as an alkali sulphide. The image obtained on the metallic sheet by application of the silver halide diffusion transfer process may further be treated in known manner in order toenhance the oleophilic and the hydrophilic characteristics of the image parts for producing a satisfactory printing plate.

It has been found however, that such nuclei or nucleilayers do not adhere properly to the metal surface, with the result that imperfect images are obtained, and/ or only a very limited quantity of readable prints are produced from the lithographic plates obtained in this way. Also the keeping qualities of such coated metal sheets are rather limited, since after a relatively short time the activity of the nuclei or nuclei-forming substances is almost completely lost. These difficulties can be eliminated to some extent if the nuclei are applied in suitable binding agents. In this case, however, the difference in affinity for the printing ink of the image and non-image areas is reduced that the conversion of the image into a lithographic image is likewise greatly impeded.

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It has now been found that these difficulties can be avoided if the nuclei heretofore used in preparing lithographic plates by the dilfusion transfer processes are omitted, and, instead, the metallic surface itself is allowed to take part actively in the reduction of the diffusing silver salts, and the silver images thus obtained are thereafter subjected to a subsequent lithographic after-treatment which increases the hydrophility of the metal support and the oleophility of the silver precipitate. In the process according to our present invention, advantage is taken of the fact that the metallic support is made of a metal or an alloy of metals which is higher than silver in the electrolytic series, and therefore is capable of exerting a strong reduction power towards silver ions. In this way, silver complexes which diffuse out of the negative during the diffusion transfer process are readily reduced by the metal surface of the lithographic plate. Metals which are commonly used as lithographic plates and are higher than silver in the electrolytic series include aluminum, zinc, magnesium, copper, lead and iron, or the alloys mainly consisting of one of these metals, such as, for example, stainless steel.

Accordingly it is one object of this invention to provide a simplified method of preparing photomechanical printing plates.

It is another object of this invention to provide a process for the transfer of a photographic image to a metallic plate by using a silver halide diffusion transfer process under such conditions that the transfer takes place readily and easily.

It is still a further object of this invention to provide a process for producing a sturdy printing plate which has good letter-sharpness and which may be used a great number of times during a printing process. Further objects of this invention will be apparent from the following description.

According to one embodiment of the present invention, an aluminum sheet and an exposed photographic material are passed through a developing apparatus normally used for diffusion transfer and filled with a developing solution which besides the usual ingredients for development of the exposed silver halide also contains a solvent for the undeveloped silver halide. On leaving the developing bath, the aluminum sheet and the exposed negative are closely pressed together. After a few moments, both elements are separated from each other and a silver image is obtained on the aluminum sheet.

It has also been found that on processing the aluminum sheet in the alkaline developing solution the naturally present oxide layer on the aluminum is removed and at the same time the diffused silver salts spontaneously are electrolytically reduced to silver on the oxide free aluminum surface.

The lapse of time between wetting the aluminum surface and its contact with the developing negative should be limited in order to obtain a good quality silver precipitate on the aluminum surface. It is evident that these objects can be achieved mechanically by arranging and suitably coordinating the processing time and the contact time of the negative material with the aluminum surface.

For carrying out the method according to the present invention the light-sensitive material involved comprises a support and an emulsion layer. Additional layers, such as an intermediate layer, a filter layer and/ or an antistress layer, may also be present.

The support may be any of the common materials heretofore used in diffusion transfer processes, however, it is preferred to use a support that is flexible, thin and dimensionally stable in order to avoid wrinkling when the support is closely pressed together onto the aluminum sheet. Suitable support materials are, among others,

-19 paper and films of cellulose derivatives or of full-synthetic polymeric substances.

The emulsion layer may be any light-sensitive silver halide emulsion,'either negative or direct positive, which gives sulficiently rapid development of the image wise exposed silver halide layer, suflicient complex formation of the non-developed silver halide and a satisfactory gradation necessary for graphic purposes. In practice mainly silver chloride emulsions are used, which contain some amounts of bromide and iodide or other ingredients, necessary for obtaining the desired emulsion characteristics.

It has also been found that the hardening degree of the emulsion layer is important in obtaining good results and should be sufiicient to obtain good and uniform adherence of the light sensitive material to the aluminum sheet during diffusion-transfer. This can be achieved by adding to the emulsion, to an intermediate layer or to an auxiliary layer, hardening agents and/ or agents which prevent hardening, according to the desired hardening degree of the material.

In addition the emulsion may contain other ingredients such as chemical and optical sensitizers, stabilizers, antifogging agents, developers and/ or development acceleraors, wetting agents, light-screening substances, etc.

The light-sensitive paper can be exposed in Contact with the original by either the reflex method or the transmitted light method. It is also possible to expose the photographic paper by optical methods employing the' usual copying cameras. More details of these methods are published in information folders for document copyists such as the data-sheet JC/ -1 published November 1954 and June 1959, and the Gevacopy booklet: Rapid Ultra-rapid Gevacopy, published November 1958, both edited by Gevaert Photo-Producten N.V., Mortsel, Belgium.

The developing bath used for carrying out the diffusion transfer process of the present invention contains the necessary ingredients for the development of the exposed (or, if a direct positive emulsion is used, for the fogged, non-exposed) silver halide and a solvent for the non developed silver halide. The developing bath may further contain other ingredients, including those generally em ployed in the art, such as substances for preventing aerial oxidation of the developendevelopment accelerators, alkali etc. obtaining special results.

Also it has been found that by adding to the developer solution an aliphatic alcohol such as ethanol, 2,2-dimethylpropane'diol-l,3 or a polyethylene glycol, suitable moistening of the exposed photographic material and of the metallic plate is obtained when they are pressed into contact with each other. 7

It has still further been found that the elimination of the oxide layer on the surface of the metallic sheet, espe cially in the case of aluminum, can be accelerated by adding to the developing solution sequestering agents, such as (poly)amino (poly)carboxylic acids or salts thereof according to the general formula Li J.

M=H, NH Na, K or amine R=an alkyl group, an aryl group, anaralkyl group,- an isocyclic'or heterocyclic nucleus, these groups being either substituted or not by halogen, hydrox'yl, ethermercapto, T"-

4 acid groups such as CO M, --PO(OM) 1=H(oM and SO M, heterocyclic groups such as, e.g., pyridine and quinoline, amine or substituted amine,

or NH either substituted or not suchv as, e.g., by two acetic acid groups, and where,

X=O, l,2,3,4, 5,6

Typical examples of such sequestering agents are:

Ethylenediamine-N,N,N',N-tetra acetic acid and salts thereof; N-fl-hydroxyethyl-N,N',N-ethylenediaminetriacetic acid; N,N-di-Z-hydroxypropyl-N',N-ethylenediaminediacetic acid; Ethylenediamine-N,N,N',N'-tetrapropionic acid; 1,2-cyclohexanediamino-N ,N,N',N-tetra acetic acid; Hydroxyethyliminodiacetic acid; Dihydroxyethylamino-acetic acid; Diethylenetriamine-N,N,N,N",N-penta acetic acid; N,'N-di-3 (di-Z hydroxyethylimino) -2-hydroxypropyl-N N-ethylene-diamino-diacetic acid; N,N,N,N'-ethylenediaminotetraphosphonic acid; 2-sulphoethyliminodiacetic acid; N-a-pyridinomethyl-NN,N'-ethylenediaminotriacetic acid; N,N'-di(o-hydroxyphenylacetic acid)-ethylenediamine; Hydrazino tetra acetic acid.

Although the exact chemical function of the sequestering agents in eliminating the metal oxide layer from the metal is not known, it is supposed that these sequestering agents counteract the inhibiting action of earth alkaline metal ions present in the tap-water on the alkaline attack process of the aluminum oxide layer.

After the formation of the silver image of the metallic plate, the plate bearing the adhering silver image is made ready for printing by rubbing it with a suitable lithographic preparation.

In this respect, it has now been found that the inkand/ or lacquer receptivity of the silver image is markedly enhanced by incorporating in the lithographic preparation one or more compounds from the following two groups of compounds which strengthen the hydrophobic properties of the metallic silver by their oleophilic groups:

(a) Quaternary ammonium compounds such as cetyltrimethyl-ammonium bromide, benzyltrimethyl ammonium bromide and dodecyl trimethyl ammonium chloride,

(b) Compounds containing a mercapto group which can react with the precipitated silver such as Z-mercaptobenzthiazole, 2,S-dimercapto-1,3,4-thiodiazole, 6-methyl- Z-mercapto benzimidazole, 2-mercapto-5-phenyl-1,3,4-oxodiazole, 1-phenyl-3-thiourazole, l-phenyl-S-mercapto tetrazolo, 5,6-dimethyl-2-mereapto-4-phenyl-1,3,4,-4H-thiadiazine and 3-imino-7,2,4-dithiazolidine-S-thione.

Since the non-printing parts of the aluminum plate oxidize quite rapidly in the air and become less hydrophilic, the lithographic plate is treated as soon as possible after the formation of the silver image with a lithographic preparation containing a polymeric substance such as gum arabic or carboxymethyl cellulose which leaves a thin hydrophilic layer on the blank metallic plate rendering the non-printing parts ink-repellent.

The ink-repellent characteristics may be further increased by addition of phosphoric acid and/ or its salts.

According to a preferred embodiment of the present invention, the printing plate bearing the silver image is treated with a lithographic preparation containing at least one compound enhancing the ink and/ or lacquer receptivity of the silver image, and containing further at least one compound preventing the oxidation of the aluminum and/ or at least one compound increasing the ink-repellent characteristics of the plate metal.

The. following examples are illustrative of the process of this invention, but should not be considered as limiting the scope thereof.

Example 1 A light-sensitive negative paper obtained by coating 21 silver chloride emulsion layer on a baryta-coated paper base of 135 g. per sq. m. is exposed to an image according to the reflex method. The exposed negative and an aluminum sheet consisting of 99.5% of aluminum and 0.5% of magnesium and silica, the surface of which was brushed to grain depths of 2 to 4 microns, are passed through an apparatus ordinarily used for the diffusion transfer process. This apparatus contains an aqueous developer solution of the following composition:

. G. Sodium hydroxide 11 Sodium sulphite 100 Sodium thiosulphate 6 Potassium bromide 1.5 Hydroquinone 9 l-phenyl-S-pyrazolidone 1 .5 Trisodium salt of ethylendiamine-tetra acetic acid 4 Water to 1000 cm.

After passing through this solution the negative and the aluminum plate are brought into contact between rubber rollers. The paper sheet carrying the emulsion layer is separated from the aluminum sheet, leaving a silver image on the aluminum sheet adhering to the surface of said sheet. Immediately thereafter, the plate bearing the image is further rubbed for about 30 seconds with a cloth, soaked with a lithographic preparation of the following composition:

Carboxymethylcellulose g 3.24 Sodium phosphate g 0.6 Phosphoric acid g 0.3 Cetyltrimethylammonium bromide g 0.06

20% aqueous solution of formaldehyde cm. 1 Water to 100 c111 The lithographic printing plate thus obtained is ready for use.

Example 2 G. Trisodium phosphate 1 Gum arabic l 1-phenyl-S-mercaptotetrazole 0.05

Water up to 100 cm.

The zinc sheet is then rubbed with a greasy lithographic ink, powdered with finely divided asphaltum powder and heated at 130 C. The parts of the plate which have not to be etched are then covered with asphaltum lacquer. The etching of the zinc sheet is then carried out according to methods known to those skilled in the art of preparing typographic printing plates.

We claim:

1. In a process for the manufacture of a silver image bearing metal plate for printing purposes by application of the silver halide difi'usion transfer process, the steps of treating a photographic material containing a light sensitive silver halide emulsion layer having exposed and nonexposed areas with a silver halide developing solution con taining a sequestering agent, wherein said sequestering agent is a compound selected from the group consisting of amino polycarboxylic acids and water soluble salts thereof, contacting the side of said photographic material bearing the emulsion layer with the surface of a metal plate in the presence of a silver halide solvent, said surface of said metal plate being substantially oxide free and composed of a metal higher than silver in the electrolytic series, whereby the undeveloped silver halide in the emulsion layer at least partially dissolves, diffuses from said emulsion layer to the surface of said metal plate, is reduced by said plate and deposits as a silver image on the surface of said metal plate. a

2. The process of claim 1 wherein said silver halide solvent is present in said silver halide developing solution.

3. The process of claim 2 wherein the surface of the metal plate on which the silver image is precipitated is aluminum.

4. The process of claim 3 wherein said aluminum surface of said metal plate has been treated with said developing solution prior to contacting said aluminum surface of said metal plate with the side of said photographic material bearing the emulsion layer.

5. The process of claim 4, wherein an aliphatic alcohol is present in said silver halide developing solution, said aliphatic alcohol being selected from the group consisting of ethanol, 2,2-dimethyl propanediol-1,3 and polyethylene glycol.

6. In a process for the manufacture of a silver image bearing metal plate for printing purposes by application of the silver halide diifusion transfer process, the steps of treating a photographic material containing a light sensitive silver halide emulsion layer having exposed and non-exposed areas with a silver.halide developing solution, contacting the side of said photographic material bearing the emulsion layer with the surface of a metal plate in the presence of a silver halide solvent, said surface of said metal plate being substantially oxide free and composed of a metal higher than silver in the electrolytic series, whereby the undeveloped silver halide in the emulsion layer at least partially dissolves and difi'uses from said emulsion layer to the surface of said metal plate and is reduced by said plate to deposit a silver image on said surface, and treating said plate bearing said silver image with a lithographic solution to increase the oleophility of said silver image, said lithographic solution containing an oleophilic compound selected from the group consisting of quaternary ammonium compounds having an oleophilic group attached thereto and mercapto compounds having an oleophilic group attached thereto and capable of reacting with precipitated silver.

7. The process of claim 6 wherein the surface of the metal plate on which the silver image is deposited is zinc.

8. The process of claim 6 wherein the surface of the metal plate on which the silver image is deposited is aluminum.

9. The process of claim 6 wherein the lithographic solution also contains a hydrophilic organic polymeric compound, forming a thin hydrophilic layer on the blank parts of the metal plate where no silver image has been formed with said hydrophilic organic polymeric compound and thereby rendering said blank parts ink-repellent.

10. The process of claim 9 wherein said hydrophilic organic polymeric compound is selected from the group consisting of carboxymethyl cellulose and gum arabic.

11. The process of claim 6 wherein the lithographic solution also contains a compound selected from the group consisting of phosphoric acid and salts of phosphoric acid, said compound rendering the blank parts of the metal plate where no silver image has been formed ink-repellent.

12. In a process for the manufacture of a silver image bearing metal plate for printing purposes by application of the silver halide diffusion transfer process, the steps of treating a photographic material containing a light sensitive silver halide emulsion layer having exposed and nonexposed areas with a silver halide developing solution containing a sequestering agent, wherein said sequestering agent is a compound selected from the group consisting of amino polycarboxylic acids and Water soluble salts thereof, contacting the side of said photographic material bearing the emulsion layer with the surface of a metal plate in the presence of a silver halide solvent, said surface of said metal plate being substantially oxide free and composed of a metal higher than silver in the electrolytic series, whereby the undeveloped silver halide in the emulsion layer at least partially dissolves and diffuses from said emulsion layer to the surface of said metal plate and is reduced by said plate to deposit a silver image on said surface, and treating said surface of said metal plate bearing said silver image with a lithographic solution to increase the oleophility of said silver image, wherein the lithographic solution contains a compound selected from the group consisting of quaternary ammonium compounds having an oleophilic group attached thereto and mercapto compounds having an oleophilic group attached thereto and capable of reacting with precipitated silver.

13. The process of claim 12 wherein the surface of the metal plate on which the silver image is deposited is aluminum.

14. The process of claim 13 wherein said aluminum surface of said metal plate has been treated with said developing solution prior to contacting said aluminum surface of said metal plate with the side of said photographic material bearing the emulsion layer.

15. The process of claim 13 wherein the lithographic solution also contains a hydrophilic organic polymeric compound, forming a thin hydrophilic layer of said hydrophilic organic polymeric compound on the blank parts of the metal plate Where no silver image has been formed and thereby rendering said blank parts ink-repellent.

16. In a process for the manufacture of a silver image bearing metal plate for printing purposes by application of the silver halide diffusion transfer process, the steps of treating a photographic material containing a light sensitive silver halide emulsion layer having exposed and non exposed areas with a silver halide developing solution containing a sequestering agent and asilver halide solvent, wherein said sequestering agent is a compound selected from the group consisting of amino polycarboxylic acids and Water soluble salts thereof, contacting the side of said photographic material bearing the emulsion layer with a substantially oxide free surface of an aluminum plate, said surface of said aluminum plate having been treated prior to said contacting with said silver halide developing solution, whereby the undeveloped silver halide corresponding to the non-exposed areas of the emulsion layer at least partially dissolves and diffuses from said emulsion layer to the surface of said aluminum plate and is reduced by said plate to deposit a silver image on said surface, and treating said surface of said aluminum plate bearing said silver image with a lithographic solution ,to increase the oleophility of said silver image and the hydrophlity of the blank parts of said aluminum plate where no silver image has been formed, said lithographic solution containing a hydrophilic organic polymeric compound and an oleophilic compound selected from the group consisting of quaternary ammonium compounds having an oleophilic group attached thereto and mercapo compounds having an oleophilic group attached thereto and capable of reacting with said deposited silver.

References Cited by the Examiner UNITED STATES PATENTS 1,742,710 1/30 Krebs 96-29 2,352,014 6/44 Rott. 2,656,273 10/53 Henn et al 9666 2,823,122 2/58 Land 9629 3,083,097 3/63 Lassig et al. 96-29 FOREIGN PATENTS 440,736 1/36 Great Britain.

59,365 5/47 Holland.

648,897 1/51 Great Britain.

565,696 3/58. Belgium. 1,064,343 8/59 Germany.

OTHER REFERENCES Agfa, German application 1,011,280, printed June 27, 1957 Kl. 57d.

Neblette: Photography, Its Materials and Processes, 5th Ed., D. Van Nostrand C0,, Inc., New York, 1952, pages 210l1.

NORMAN G. TORCHIN, Primary Examiner.

MILTON STERMAN, HAROLD N. BURSTEIN, WIL- LIAM B. KNIGHT, Examiners. 

1. IN A PROCESS FOR THE MANUFACTURE OF A SILVER IMAGE BEARING METAL PLATE FOR PRINTING PURPOSES BY APPLICATION OF THE SILVER HALIDE DIFFUSION TRANSFER PROCESS, THE STEPS OF TREATING A PHOTOGRAPHIC MATERIAL CONTAINING A LIGHT SENSITIVE SILVER HALIDE EMULSION LAYER HAVING EXPOSED AND NONEXPOSED AREAS WITH A SILVER HALIDE DEVELOPING SOLUTION CONTAINING A SEQUESTERING AGENT, WHEREIN SAID SEQUESTERING AGENT IS A COMPOUND SELECTED FROM THE GROUP CONSISTING OF AMINO POLYCARBOXYLIC ACIDS AND WATER SOLUBLE SALTS THEREOF, CONTACTING THE SIDE OF SAID PHOTOGRAPHIC MATERIAL BEARING THE EMULSION LAYER WITH THE SURFACE OF A METAL PLATE IN THE PRESENCE OF A SILVER HALIDE SOLVENT, SAID SURFACE OF SAID METAL PLATE BEING SUBSTANTIALLY OXIDE FREE AND COMPOSED OF A METAL HIGHER THAN SILVER IN THE ELECTROLYTIC SERIES, WHEREBY THE UNDEVELOPED SILVER HALIDE IN THE EMULSION LAYER AT LEAST PARTIALLY DISSOLVES, DIFFUSES FROM SAID EMULSION LAYER TO THE SURFACE OF SAID METAL PLATE, IS REDUCED BY SAID PLATE AND DEPOSITS AS A SILVER IMAGE ON THE SURFACE OF SAID METAL PLATE. 